The present invention relates to a communication system suitably applied to a case wherein a signal transmitted by, e.g., a predetermined communication network is wireless-transmitted to a mobile station and, more particularly, to a case wherein digital data is transmitted in an asynchronous transfer mode.
As a digital data transmission process, an asynchronous transfer mode (to be referred to as an ATM hereinafter) is known. This ATM asynchronously transmits various digital data. Here, an ATM communication network developed to perform conventional ATM transmission is to perform transmission with a wire transmission path. In addition, the ATM communication network is designed on the assumption that data is transmitted with a high-quality signal line such as an optical fiber cable having small transmission degradation.
In contrast to this, there is a demand that ATM communication should be performed even in mobile communication. For this reason, it is considered that the ATM communication network should be connected to a wireless communication network. FIG. 13 is a view showing an example of a conventional arrangement obtained when end-end communication is performed between a terminal device 1 connected to the ATM communication network and a terminal device 4 connected to a mobile station. The terminal device 1 is connected to an ATM network b with a user-network interface a, and a radio base station 2 for performing wireless communication is connected to the ATM network b with a user-network interface c. A mobile station 3 for performing wireless communication with an air interface d is prepared, and the mobile station 3 is connected to the terminal device 4 with a user-network interface e. The radio base station 2 and the mobile station 3 comprise transmission/reception antennas 2a and 3a, respectively.
The radio base station 2 performs a conversion process between an ATM cell used in the ATM network and a wireless communication format. The mobile station 3 performs a conversion process between the air interface d and the user-network interface e.
Here, an example of an arrangement of an ATM cell serving as a format of a signal transmitted through an ATM network is shown in FIGS. 2 and 3. In transmission in an asynchronous transfer mode, one unit of signal is defined as a signal of a unit called a cell. One unit of ATM cell 100 is constituted by a header information portion 110 and a user information portion 120 as shown in FIG. 2. In this example, one unit of ATM cell 100 consists of 53 bytes. The start header information portion 110 has 5 bytes, and the subsequent user information portion 120 has 48 bytes.
The detail example of the format of one unit of ATM cell 100 is shown in FIG. 3. Four bits of the first octet are bits of generic flow control (GFC) 111, eight bits including four bits of the first octet and four bits of the second octet are bits of virtual path identifiers (VPIs) 112 and 113. Sixteen bits including the second four bits of the second octet to the first four bits of the fourth octet are bits of a virtual channel identifier (VCI) 114, and three bits of the fourth octet are bits of a payload type (PT) 115. One bit of the fourth octet is a bit of a cell loss priority (CLE) 116, and eight bits of the fifth octet are bits of a header error control information (HEC) 117. The arrangement described above is the arrangement of the header information portion 110. Forty-eight bits of the sixth octet to the 53rd octet denote a user information region 120. In this specification, user information transmitted in the user information region is called a payload.
Of the data in the header information portion 110, data for determining a routing of an ATM cell are the virtual path identifiers (VPIs) 112 and 113 and the virtual channel identifier (VCI) 114. An 8-bit (1 byte) header error control information (HEC) 117 is constituted by a cyclic redundancy check (to be referred to as a CRC hereinafter) serving as an error detection signal. The CRC is a code given to be generated from 4-byte header information of the first octet to the fourth octet, and functions to protect the header information in this partition. The header error control information (HEC) 117 also has a cell-synchronization function of specifying the position of a cell in an arbitrary byte string.
In 1-byte information constituting the header error control information (HEC) 117, 4-byte header information of the first octet to the fourth octet is regarded as a 31-order polynomial on the transmission side. The 31-order polynomial is multiplied by X8, the product is divided by a polynomial X8+X2+X+1 to obtain remainder. A value obtained by adding xe2x80x9c01010101xe2x80x9d to the remainder is defined as header error control (HEC). On the reception side, xe2x80x9c01010101xe2x80x9d is added to a value of the header error control (HEC), and the resultant value is divided by the same polynomial as that on the transmission side to obtain a remainder. If the remainder is not 0, it is determined that an error is detected.
As described above, data is transmitted as formatted data through an ATM network. However, in the air interface d shown in FIG. 13, the data must be transmitted in a format for wireless transmission. More specifically, as described above, the ATM network is basically a network used in a state wherein line quality is good, and the header error control (HEC) added to the header information has a very simple arrangement having a small number of bits as an error correction code. The payload transmitted in the user information region is transmitted without adding an error detection code to the payload. In contrast to this, when data is transmitted by a radio circuit, a transmission error is probably generated for various factors. The data must be transmitted while an error detection code having check capability which is high to some extent is added to the data. In the radio base station 2, format conversion is made to add the error detection code to the data.
An example of a signal wireless-transmitted between the radio base station 2 and the mobile station 3 is shown in FIG. 14. Referring to FIG. 14, a case wherein data transmission is performed by using a slot having a predetermined fixed length in a time division multiplex access (TDMA) scheme. In this example, data of one ATM cell is allocated to one slot 200. In the slot 200, one slot consists of 67 bytes, and a 4-byte preamble (PR) 201 for slot synchronization, a 4-byte unique word (UW) 202 representing the start of data, and a 2-byte control signal (CAC) 203 are sequentially arranged. The subsequent 53-byte partition is defined as a user information partition. In this example, a 5-byte header information portion 204 of the ATM cell and a 48-byte ATM payload 205 are arranged. As the 5-byte header information portion 110 and the 48-byte ATM payload 205, the 5-byte header information portion 204 and the 48-byte payload 120 shown in FIG. 3 are directly arranged. An error detection code 206 (CRC) is added to the last four bytes of the slot 200. The error detection code 206 is a code generated for data of a partition ranging from the control signal (CAC) to the ATM payload. As the code, a code having relatively high check capability is used.
The example in FIG. 14 is obtained when data of one ATM cell can be arranged in a user information partition of one slot. However, the length of one slot may be shortened, and the data of one ATM cell may be wireless-transmitted. FIG. 15 is a view showing an example of this case. In this example, two slots 210 and 220 each having a slot length of 50 bytes are used. In the slots 210 and 220, from the start, 4-byte preambles (PRs) 211 and 221, 4-byte unique words (UWs) 212 and 222, and 4-byte control signals (CACs) 213 and 223 are sequentially arranged. In a 36-byte user information partition, a 5-byte ATM header 214 of the first cell is arranged. An ATM payload 215 of the first cell is arranged as the remaining 31 bytes. At this time, since the payload of one ATM cell has 48 bytes, the remaining 17 bytes of the payload of the first cell are arranged as an ATM payload 224 of the first cell at the start portion of the user information partition of the next slot 220. An ATM header 225 of the next cell (second cell) and a 14-byte ATM payload 226 of the second cell are arranged at the remaining portion of the user information partition of the slot 220. The remaining payload of the second cell is arranged in the user information partition (not shown) of the next slot. Error correction codes (CRCs) 216 and 227 are arranged as the last four bytes of the slots 210 and 220, respectively.
As described above, in any cases, the header information and payload of the ATM cell are constituted such that all the data are directly wireless-transmitted.
However, it is not preferable in data transmission efficiency that header information of a cell to be transmitted through an ATM network is directly arranged and transmitted to a slot in wireless transmission. More specifically, the header information is originally used for control, and is added to correctly transmit the payload. On the other hand, a slot or the like determined by a wireless transmission format is designed to transmit control information. For example, in the slot arrangements shown in FIGS. 14 and 15, preambles PR, unique words UW, and both of control information for slot transmission of the control signal CAC and ATM headers are transmitted. In the arrangement, control information is duplex-transmitted. As described above, when many pieces of control information must be transmitted, a capacity being capable of transmitting a payload serving as actual user information decreases.
The present invention has been made in consideration of the above circumstances, and has as its object to efficiently transmit a payload serving as user information when data transmitted by a predetermined wire transmission path such as an ATM network is wireless-transmitted.
According to the first aspect of the present invention, there is provided a communication system constituted by a transmission device and a reception device, wherein the transmission device comprises: first reception means for receiving a transmission signal of a first data amount unit of a first format including first header information including a first error correction signal and first user information transmitted by a first transmission path; when information obtained by removing the first error correction signal from the first header information of the transmission signal of the first format received by the first reception means is used as second header information, and the first user information itself is used as a second user information, transmission signal generation means for generating a transmission signal of a second format by adding a second error correction signal serving as an error correction signal for a signal of a second data amount unit to the signal of the second data amount unit including at least one of the second header information and the second user information; and transmission means for transmitting the transmission signal of the second format to a second transmission path, and the reception device comprises: second reception means for receiving the transmission signal of the second format transmitted by the second transmission path; error correction means for performing error correction for the signal of the second data amount unit on the basis of the second error correction signal included in the transmission signal of the second format received by the second reception means; error correction signal generation means for generating a third error correction signal serving as an error correction signal for the second header information corrected by the error correction means; and transmission signal generation means for generating the transmission signal of the first format from header information including the third error correction signal and the second user information.
According to the second aspect of the present invention, there is provided a transmission device comprises: first reception means for receiving a transmission signal of a first data amount unit of a first format including first header information including a first error correction signal and first user information transmitted by a first transmission path; when information obtained by removing the first error correction signal from the first header information of the transmission signal of the first format received by the first reception means is used as second header information, and the first user information itself is used as a second user information, transmission signal generation means for generating a transmission signal of a second format by adding a second error correction signal serving as an error correction signal for a signal of a second data amount unit to the signal of the second data amount unit including at least one of the second header information and the second user information; and transmission means for transmitting the transmission signal of the second format to a second transmission path.
According to the third aspect of the present invention, there is provided a reception device for receiving a transmission signal of a second format from a transmission device which comprises: first reception means for receiving a transmission signal of a first data amount unit of a first format including first header information including a first error correction signal and first user information transmitted by a first transmission path; when information obtained by removing the first error correction signal from the first header information of the transmission signal of the first format received by the first reception means is used as second header information, and the first user information itself is used as a second user information, transmission signal generation means for generating the transmission signal of the second format by adding a second error correction signal serving as an error correction signal for a signal of a second data amount unit to the signal of the second data amount unit including at least one of the second header information and the second user information; and transmission means for transmitting the transmission signal of the second format to a second transmission path, comprising: second reception means for receiving the transmission signal of the second format transmitted by the second transmission path; error correction means for performing error correction for the signal of the second data amount unit on the basis of the second error correction signal included in the transmission signal of the second format received by the second reception means; error correction signal generation means for generating a third error correction signal serving as an error correction signal for the second header information corrected by the error correction means; and transmission signal generation means for generating the transmission signal of the first format from header information including the third error correction signal and the second user information.
According to the fourth aspect of the present invention, there is provided a communication method between a transmission device and a reception device, comprising the steps of: causing the transmission device to receive a transmission signal of a first data amount unit of a first format including first header information including a first error correction signal and first user information transmitted by a first transmission path; causing the transmission device, when information obtained by removing the first error correction signal from the first header information of the transmission signal of the first format received by the first reception means is used as second header information, and the first user information itself is used as a second user information, to generate a transmission signal of a second format by adding a second error correction signal serving as an error correction signal for a signal of a second data amount unit to the signal of the second data amount unit including at least one of the second header information and the second user information; transmitting the transmission signal of the second format from the transmission device to a second transmission path; causing the reception device to receive the transmission signal of the second format transmitted by the second transmission path; causing the reception device to perform error correction for the signal of the second data amount unit on the basis of the second error correction signal included in the transmission signal of the second format received by the second reception means; causing the reception device to generate a third error correction signal serving as an error correction signal for the second header information corrected by the error correction means; and causing the reception device to generate the transmission signal of the first format from header information including the third error correction signal and the second user information.
According to the fifth aspect of the present invention, there is provided a transmission device comprising: a reception unit for receiving a signal obtained by transmitting header information and user information as a signal of a first format by a first wire transmission path; a determination unit for determining that the same header information is repeated every predetermined unit by the reception unit; transmission data generation unit for arranging the header information and the user information received by the reception unit in a user information partition of a second format being appropriate for a second wireless transmission path to generate transmission data, and omitting the second and subsequent arrangements of the same header information when the determination unit determines the repetition of the same header information; and a transmission unit for transmitting the transmission data generated by the transmission data generation unit to the second transmission path.